Light-emitting elements such as a light-emitting diode (hereinafter, referred to as a “LED”) are used in various types of light-emitting devices. The LED may replace an existing light source that uses discharge and radiation, due to the recently increased luminous flux, as well as the smaller size and higher efficiency compared with those of the existing light source. Furthermore, the LED is smaller in size compared with the light source using discharge and radiation, so that the LED has advantages in the applicability to increased applications, the ease of handling, the expectation of various designs, and the like. Thus, the LED is a light source having increased added values.
Furthermore, the LED is capable of controlling the radiation pattern of emitted light, in combination with an optical system having a reflection function and a lens function. Furthermore, if a LED chip measuring several mm per side is used, the chip can be considered as a small point light source, so that the optical system also can be miniaturized.
Meanwhile, when a white LED is formed by combining the LED chip with a wavelength converting layer including a phosphor that converts a wavelength of a part of light from the LED chip, the wavelength converting layer, as well as the LED chip, also is considered as a light-emitting portion. Accordingly, the light-emitting portion becomes larger in size than the LED chip.
In order to make the best possible use of an amount of light emitted from the light-emitting portion as light to be emitted from the light-emitting device, it is desirable that the optical system to be used has a sufficiently larger size than the light-emitting portion or that the light-emitting portion have sufficiently smaller dimensions than the optical system. In order to make the optical system as small as possible so as to achieve a smaller and thinner light-emitting device, the wavelength converting layer has to be as small as possible. As a known structure that makes the wavelength converting layer smaller in size, Patent Document 1 and Patent Document 2 below disclose a structure in which a resin paste in which a high concentration of phosphor is dispersed is used to form the wavelength converting layer three-dimensionally around the LED chip.
Patent Document 1: JP 2001-135861 A
Patent Document 2: U.S. Pat. No. 6,650,044
A general white LED obtains white light by synthesizing emitted light from the LED chip and converted light from the wavelength converting layer. Alternatively, the converted light from the wavelength converting layer may be white light. In the structure disclosed in Patent Documents 1 and 2, since a high concentration of phosphor is present around the LED chip, the emitted light from the LED chip and the converted light obtained by the phosphor are blocked by the phosphor, resulting in a smaller amount of light passing through the wavelength converting layer. Further, a part of the emitted light from the LED chip may be reflected by the phosphor and reabsorbed into the LED chip or absorbed into an electrode of the LED chip. Thus, the efficiency of extracting white light may be decreased.
In order to extract white light with high efficiency, the concentration of the phosphor may be reduced. However, this makes the wavelength converting layer and, accordingly, the optical system larger in size, thereby serving to hamper achieving the object of obtaining a smaller and thinner light-emitting device.